This application incorporates by reference Taiwan application Serial No. 89219805, filed Nov. 15, 2000.
1. Field of the Invention
The invention relates in general to an apparatus adaptable for two scanning resolutions, and more particularly to dual-carriage scanning apparatus.
2. Description of the Related Art
As the technology progresses, the integration and application of multimedia have become the current trend. With increases in performance and decreases in price, multimedia is now commonplace. Multimedia, so to speak, is the use of computers to present different types of information, such as text, images and sound, in an integrated way. There are several kinds of multimedia devices developed for capturing and presenting images or sound. As for image processing, the scanning apparatus is a common tool for users to capture images.
Referring to FIG. 1A, a perspective view of a conventional flatbed scanner is shown. The flatbed scanner includes a scanning bed 102 and a cover 104. The scanning bed 102 has a platform 106. The glass plate 108 positioned on the scanning bed 102 is capable of placing the document to be scanned 111. The cover 104 is coupled to the scanning bed 102 by hinge 110. The document to be scanned 111 is first placed on the scanning bed 106. After the cover 104 is closed, the carriage (not shown in FIGs) disposed inside the scanning bed 106 is driven to sense the image of the document to be scanned 111 and start to scan.
Referring to 1B, a lateral sectional view of the conventional flatbed scanner in FIG. 1A is shown. As shown in FIG. 1B, the scanning bed 102 has a carriage 112. The carriage 112 is capable of scanning the image of the document to be scanned 111. The carriage 112 includes a lens 116 and a sensing module 118. The lamp 114 positioned in the carriage 112 provides the illumination for scanning. In case the document to be scanned is a reflective document, the image formation in reflective scanning mode is as follows. The light generated from the lamp 114 is first reflected by the document to be scanned 111, the reflected light is then entering the lens 116. It can form the image of the document to be scanned 111 on the sensing module 118 by focusing the lens 116. The sensing module 118 transforms the received image signals to electric signals for processing and reads the image information sensed. There are various kinds of sensing module such as the CCD (Charge Coupled Device) or CIS (Contact Image Sensor) equipped with the above-mentioned function.
After reading the image signals, the stepping motor (not shown in FIGs) drives the carriage 112 to move slightly toward the area to be scanned and then the sensing module 118 reads the next image information sensed. Repeating the foregoing steps can finish the scan of the document to be scanned 111. In case the document to be scanned is a transmissive document, the image formation principle can be also applied. What needs to be noticed, the distinction of the transmissive scanning mode is utilizing the lamp 114 positioned in the cover 104. The light generated from the lamp 114 passes through the document to be scanned 111 and the image of the document to be scanned 111 is formed on the sensing module 118.
Referring to FIG. 2, the distance between the object and the lens and the distance between the lens and the optical sensing module are shown. As shown in FIG. 2, the distance between the lens 202 and the sensing module 204 is m and the optical length between the lens 202 and the document to be scanned 206 is n. The distance m and the optical length n are the determinants of the resolution of the carriage. Any variation in the distance m or the optical length n can change the scanning resolution.
Most scanners available today are capable of producing images at a single resolution. A scanning apparatus with changeable resolution has been disclosed in Taiwan Publication No. 233829, which utilizes the variation in the distance m to provide different resolutions. In the structure of the carriage, however, the distance m between the lens 202 and the sensing module 204 is very short. It requires not only high-precision stepping motor but also high-precision instrument to drive the stepping motor. It increases the difficulty of the accuracy adjustment and the cost of manufacture.